Watch out Portland, the Romans are coming

Portland cement dominates construction in the modern era. It's the “glue” that holds most modern concrete together, but making it releases a significant amount of carbon dioxide -  generating the 1,450º necessary to heat the mix of limestone and clay requires large amounts of fuel, during which process the heated limestone releases an additional batch of calcium carbonate.

All in all, the industrial manufacture of concrete produces an enormous amount of CO2. By more than one estimate, annual worldwide production creates between 5-10% of all atmospheric CO2,  and with the increasing demand for it expressed in the developing world, it this figure is set to rise.

That is, unless we return to making it like the Romans did 2000 years ago.

It's well known that the Romans used a form of concrete, however it is only recently that academics have discovered exactly how the best of the Roman version was made.

Paulo Monteiro, a professor of civil and environmental engineering at the University of California - Berkeley, led a team that discovered a 2,000-year-old breakwater in the Mediterranean Sea that was produced using a fraction of the energy - only 900º C - required to create modern concrete, the final product of which is far more durable by comparison. Considering the current predicament of carbon-induced climate change in a world in which releasing CO2 seems the dominant by-product of choice for wealth creators, this ancient concrete recipe could dramatically slash the construction industry’s emissions.

The Romans mixed lime and volcanic rock for regular concrete structures, while underwater structures were made with lime and volcanic ash that formed a mortar. When this mix connected with seawater, a hot chemical reaction occurred that cemented the lime and ash mixture. The secret ingredient is aluminum-rich pozzolan ash and it turns out that oil-producing Saudi Arabia has a lot of it.

“For us, pozzolan is important for its practical applications,” says Monteiro. “It could replace 40 percent of the world’s demand for Portland cement. And there are sources of pozzolan all over the world. Saudi Arabia doesn’t have any fly ash, but it has mountains of pozzolan.”

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Image: Jean-Christophe Benoist - licensed under creative commons.